text: A metering pump moves a precise volume of liquid in a specified time period providing an accurate volumetric flow rate. 
  Delivery of fluids in precise adjustable flow rates is sometimes called metering.  The term "metering pump" is based on the application or use rather than the exact kind of pump used, although a couple types of pumps are far more suitable than most other types of pumps.
  Although metering pumps can pump water, they are often used to pump chemicals, solutions, or other liquids.  Many metering pumps are rated to be able to pump into a high discharge pressure.  They are typically made to meter at flow rates which are practically constant (when averaged over time) within a wide range of discharge (outlet) pressure.  Manufacturers provide each of their models of metering pumps with a maximum discharge pressure rating against which each model is guaranteed to be able to pump against.  An engineer, designer, or user should ensure that the pressure and temperature ratings and wetted pump materials are compatible for the application and the type of liquid being pumped.  
  Most metering pumps have a pump head and a motor.  The liquid being pumped goes through the pump head, entering through an inlet line and leaving through an outlet line.  The motor is commonly an electric motor which drives the pump head.